Absorption heat pumps use an ammonia-water absorption cycle, as opposed to a vapor-compression cycle, to transfer heat. Ammonia may be the refrigerant, and water will be the absorber. The ammonia condenses at one of the system’s coils to release heat and evaporates at one other coil to soak up heat. https://1001bookmarks.com/story20149409/not-known-details-about-heat-pumps